U.S. patent application number 11/814040 was filed with the patent office on 2008-06-12 for device and method for preparing a homogeneous mixture consisting of fuel and oxidants.
This patent application is currently assigned to WEBASTO AG. Invention is credited to Robert Engel, Stefan Kah, Andreas Lindermeir.
Application Number | 20080134580 11/814040 |
Document ID | / |
Family ID | 36097051 |
Filed Date | 2008-06-12 |
United States Patent
Application |
20080134580 |
Kind Code |
A1 |
Kah; Stefan ; et
al. |
June 12, 2008 |
Device and Method For Preparing a Homogeneous Mixture Consisting of
Fuel and Oxidants
Abstract
A device for providing a homogenous mixture of fuel and oxidant
including an arrangement (5) for feeding liquid fuel to an
evaporator, an arrangement (4) for feeding gaseous oxidant into a
mixing zone (12) downstream of the evaporator, and a reaction zone
downstream of the mixing zone in which a packed structure (3) is
arranged. The packed structure can be a ceramic cylindrical molding
having a diameter in the range 25 to 35 mm and an axial length in
the range 15 to 50 mm or it can have flow conduits that are square
in cross-section and have a cell density in the range 400 to 1200
cpsi.
Inventors: |
Kah; Stefan;
(Neubrandenburg, DE) ; Lindermeir; Andreas;
(Goslar, DE) ; Engel; Robert; (Torgelow,
DE) |
Correspondence
Address: |
ROBERTS, MLOTKOWSKI & HOBBES
P. O. BOX 10064
MCLEAN
VA
22102-8064
US
|
Assignee: |
WEBASTO AG
Stockdorf
DE
|
Family ID: |
36097051 |
Appl. No.: |
11/814040 |
Filed: |
December 13, 2005 |
PCT Filed: |
December 13, 2005 |
PCT NO: |
PCT/DE2005/002254 |
371 Date: |
January 10, 2008 |
Current U.S.
Class: |
48/197FM ;
422/211; 422/222; 422/600 |
Current CPC
Class: |
C01B 2203/1247 20130101;
C01B 2203/1276 20130101; F23D 2212/10 20130101; C01B 2203/1288
20130101; F23D 3/40 20130101; B01B 1/005 20130101; C01B 3/386
20130101; F23D 2203/102 20130101; F23D 2203/107 20130101; F23D
2212/20 20130101; C01B 2203/0261 20130101; B01J 19/2485 20130101;
B01J 4/002 20130101; C01B 2203/1023 20130101; B01J 19/26 20130101;
F23D 2203/105 20130101; B01J 2208/00849 20130101 |
Class at
Publication: |
48/197FM ;
422/211; 422/222; 422/190 |
International
Class: |
C10L 3/10 20060101
C10L003/10; B01F 3/02 20060101 B01F003/02; B01J 19/24 20060101
B01J019/24 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 14, 2005 |
DE |
10 2005 001 900.5 |
Claims
1-10. (canceled)
11. A device for providing a homogenous mixture of fuel and oxidant
including means for feeding liquid fuel to an evaporator, means for
feeding gaseous oxidant into a mixing zone downstream of the
evaporator, and a reaction zone downstream of the mixing zone,
wherein in a packed structure is arranged in the reaction zone.
12. The device as set forth in claim 11, wherein the packed
structure comprises a cylindrical ceramic molding having a diameter
in the range 25 to 35 mm and an axial length in the range 15 to 50
mm.
13. The device as set forth in claim 11, wherein the packed
structure comprises flow conduits with a square cross-section
having a cell density in the range 400 to 1200 cpsi.
14. The device as set forth in claim 11, wherein at least in part a
surface of the packed structure has a catalytic coating.
15. The device as set forth in claim 11, wherein the reaction zone
is followed by a homogenization zone.
16. The device as set forth in claim 11, wherein the homogenization
zone is followed by a second reaction zone.
17. The device as set forth in claim I 1 wherein a defined air
ratio below 0.5 is provided in the mixing chamber.
18. The device as set forth in claim 11, wherein the device is
adapted to limit temperatures in an evaporation zone located
between the evaporator and the mixing zone to temperatures that
essentially do not exceed an end boiling point of the fuel.
19. The device as set forth in claim 18, wherein the evaporation
zone and the mixing zone have volumes which cause residence times
of the fuel oxidant mixture, on average, to be of the magnitude of
reaction times of oxidation reactions produced.
20. A method for providing a homogenous mixture of fuel and oxidant
including the steps: feeding liquid fuel to an evaporator, feeding
gaseous oxidant and evaporated fuel into a mixing zone downstream
of the evaporator, forming a mixture by mixing oxidant and fuel in
the mixing zone, and introducing the mixture formed in the mixing
zone into a reaction zone in which a a packed structure is arranged
and through which the mixture is passed to a homogenization zone.
the homogenization zone is followed by a second reaction zone.
21. The device as set forth in claim 20, wherein a defined air
ratio below 0.5 is provided in the mixing zone.
22. The device as set forth in claim 20, wherein the device is
operated so as to limit temperatures in an evaporation zone located
between the evaporator and the mixing zone to temperatures that
essentially do not exceed an end boiling point of the fuel.
23. The device as set forth in claim 22, wherein the fuel oxidant
mixture is caused to have average residence times in the mixing
zone that are of the magnitude of reaction times of oxidation
reactions produced.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to a device for providing a homogenous
mixture of fuel and oxidant including means for feeding liquid fuel
to an evaporator, means for feeding gaseous oxidant into a mixing
zone downstream of the evaporator, and a reaction zone downstream
of the mixing zone. The invention also relates to a method for
providing a homogenous mixture of fuel and oxidant including the
steps of: feeding liquid fuel to an evaporator, feeding gaseous
oxidant and evaporated fuel into a mixing zone downstream of the
evaporator, mixing oxidant and fuel in the mixing zone and
introducing the mixture having materialized in the mixing zone into
a reaction zone.
[0003] 2. Description of Related Art
[0004] Presently, liquid fuels, such as diesel, fuel oil, gasoline,
and kerosene represent the most important source of energy for
generating heat, mechanical work and electric current, this also
being used, e.g., in automotive engine combustion and
engine-independent heating and in domestic burners. By contrast, in
fuel cell systems liquid hydrocarbons are not totally combusted,
but are converted into hydrogen by partial oxidation reactions.
Common to both types of reactions is that the liquid fuel first
needs to be converted into a gas phase and mixed with air in a
mixing chamber before then being converted in the reaction chamber.
Strived for in this technology is an optimum homogenous fuel/air
mixture since, with increased homogeneity, the proportion of
unwanted emissions, in the form of, e.g., soot, NO, and CO, can be
reduced. Carbon Monoxide, as a reaction product, is wanted in the
scope of a reaction product while it is unwanted as a product of
the combustion process.
[0005] In modern types of burners and oxidation reactors, the
mixing chamber and the reaction chamber are often separated from
each other by a molecular seal (mol seal) so that, when using
self-igniting fuels, the oxidation reaction does not already
commence within the mixing chamber with negative effects.
[0006] Evaporating the liquid fuel can be performed by a variety of
methods.
[0007] From German patent DE 39 146 11 C2, for instance, it is
known for the fuel in vehicle heaters to be evaporated on the
surface of non-woven metal fiber mats or similarly structured
surfaces, for example, woven material, whereby the liquid fuel is
applied to a hot non-woven metal fiber mat where it is distributed
and then evaporated. After evaporation, the fuel is mixed with air
and homogenized in a mixing chamber. In this arrangement, the
supply of air for combustion in the combustion chamber occurs in
steps through a plurality of air inlet ports in the combustion
chamber wall where flames can form, and due to the conduction of
heat, radiation and convection, the necessary heat is ultimately
provided for evaporation.
[0008] Evaporating fuel by means of non-woven metal fiber mats has
drawbacks, however. Measurements of the evaporation of diesel fuel
indicated very high surface temperatures (as high as 1100.degree.
C.) on a non-woven metal fiber mat, i.e., particularly above
400.degree. C., a temperature at which cracking reactions occur to
a remarkable degree causing soot production. The drawback here is
that the fuel comes into contact with the air only at the surface
of the non-woven mat and can thus oxidize. In addition, because of
the stepped air supply, most of the combustion air is supplied
mainly after evaporation on the non-woven mat. The corresponding
low air ratio at the surface of the non-woven mat results in
deposits forming on the evaporator which make stable operation
difficult and diminishes the useful life. Reaction conditions exist
comparable to those in steam cracking, resulting in the system
becoming clogged with soot as briefly explained below.
[0009] Steam cracking is a method of thermal cracking employed in
petrochemistry, in the presence of steam, naptha, a light gasoline
fraction, usually being non-catalytically cracked with steam at
approx. 800-1400.degree. C. within an externally fired coiled
cracking tubing to generate reactive low molecular compounds of
ethene and propene. Further, side products formed which are
technically interesting include, among other things, aromates
(benzol, toluol, xylol). The object in steam cracking is to produce
short-chain olefins needed in the chemical industry. As evident
from FIG. 4, these are not formed until high temperatures are
attained. Forming ethene from ethane is made easier at temperatures
exceeding approx. 700.degree. C. and forming ethine from ethene
occurs at above 1200.degree. C. This is why it is understandable
that, to produce ethene and propene, temperatures of 800 to
900.degree. C. (mean temperature pyrolysis) are employed while
forming acetylenes is performed at temperatures exceeding
1300.degree. C. (high temperature pyrolysis). It is likewise
evident from FIG. 4 that the hydrocarbons tend to dissociate into
the elements C (soot) and H. To reduce the extent of these unwanted
knock-on reactions, after the optimum reaction time (0.2 to 0.5 s),
the reaction mixture needs to be sufficiently cooled as quickly as
possible (0.1 s) so that the rate at which these unwanted products
is formed is near zero, resulting in the product composition being
kept in check not, by thermodynamic equilibrium, but by slowing
down the kinetics.
[0010] The cited compounds are, however, highly reactive under the
operating conditions that predominant in steam cracking and tend
toward condensation and polymerization reactions, resulting in the
end in soot being formed and clogging up the reaction coils to the
detriment of the corresponding heat throughput, and thus, requiring
cracking coils to be regularly replaced. Steam is added to ensure a
good radial distribution of heat in the coils by reduction of the
partial pressure to promote formation of cracked products by
ensuring a conversion of the previously formed, unwanted higher
molecular compounds (coke).
[0011] Cracking reactions can also be catalyzed heterogeneously,
for instance, by surface metal atoms, so-called active centers. The
catalytic effect of, e.g., nickel, iron, cobalt in steam reforming
methane and other hydrocarbons is described in Applied Catal. A Gen
212 (2001) 17-60 by C. H. Bartholomew.
[0012] At such correspondingly high temperatures in the evaporator,
pyrolysis reactions take place in the gas phase. Particles and
precursors of soot having formed previously on catalytically active
surfaces (non-woven mat, evaporator or combustion chamber wall,
glow pencil) can speed up this process of homogenous soot
clogging.
[0013] Soot formation in an evaporator or combustion chamber can
negatively influence the evaporator and combustion response,
resulting in higher emissions of soot, CO, hydrocarbons, smoke, and
aerosols as well as polycyclic aromatics, thus necessitating
regular regeneration strategies to get rid of the soot in the
evaporator and combustion chamber. The soot is mostly removed by
burning it off. requiring the combustion chamber to be
correspondingly designed. Because this process at correspondingly
high temperatures is kept in check by the transport of the
substances involved, the soot and oxidant need to be in contact in
the combustion chamber for a long time which may require the
combustion chamber volume to be increased accordingly. Furthermore,
exceptionally high temperatures can materialize at the surfaces of
the combustion chamber, having a negative effect on the material
properties and useful life thereof.
[0014] Temperatures sensed as high as 1100.degree. C. at the
non-woven metal fiber mats and their ambience make for heavy
demands on the material stability of the metal fibers and the
adjoining components (e.g., glow pencil, mixing chamber).
[0015] Unlike fuel evaporation by means of a non-woven metal fiber
mat, the cold flame principle as known from European Patent
Application EP 1 102 949 B1 and corresponding U.S. Pat. No.
6,793,693 is based on evaporation of the fuel in an air stream
preheated to approx. 300.degree. C. The oxidation reactions
occuring thereby are equilibrium reactions with oxygen conversion
below 20% so that the resulting gas mixture has an outlet
temperature of approx. 480.degree. C.
[0016] Cold flame evaporators have the disadvantage that the
evaporator air needs to be heated by means of a further system
component (e.g., electric heater, burner) to temperatures of
approx. 300 to 500.degree. C. so that the cold flame reaction (low
temperature oxidation) can kick in, to thus avoid spontaneous
self-ignition of the fuel/air mixture as occurs at high
temperatures. However, in spite of this, preheating of the air is
not conducive to fast cold starting and is adverse to dynamic
operation.
[0017] Although the fuel/air mixtures produced by means of
evaporators or nozzles can be safeguarded against spontaneous
self-ignition in the evaporator by mol seals between the evaporator
and the downstream reaction space (combustion, partial oxidation)
this adds to the complexity.
SUMMARY OF THE INVENTION
[0018] The invention is thus based on the object of providing a
device and a method for providing a homogenous mixture of fuel and
oxidant using non-woven mat evaporation while overcoming the
drawbacks of the prior art, at least in part.
[0019] The invention is a sophistication of the generic device in
that, in the reaction zone, a packed structure is now arranged at
the surface of and/or within which oxidation reactions occur which,
due to their exothermic response, maintain the packed structure at
the operating temperature. Part of the heat liberated is used in
the evaporation zone downstream of the evaporator for
self-maintenance of the evaporation process; the remainder of the
thermal energy is discharged with the product stream. Preferably,
partial oxidation of the fuel components (C.sub.xH.sub.y) occurs
which otherwise could prompt soot formation, for example, aromatics
and long-chain hydrocarbons C.sub.xH.sub.y with x>4 liquid at
room temperature.
[0020] Advantageously, the packed structure is configured as a
ceramic cylindrical molding having a diameter in the range 25 to 35
mm and an axial length in the range 15 to 50 mm so that the packed
structure is sized compatible with the compact configuration of the
device in accordance with the invention. For example, the diameter
is 30 mm and the axial length is, for example, 20 mm. In addition
to using ceramic materials, for example, cordierith, metallic
packed structures are also possible. As ceramic materials use can
be made, for example, of oxides of silicon, aluminum, alkaline
metals (e.g., sodium), alkaline earth metals (e.g., magnesium),
heavy metals (e.g., barium), rare earths (e.g., yttrium)
respectively mixtures thereof. A preferred ceramic is, for example,
cordierith. In addition, non-oxidic ceramics such as, for example,
carbides (e.g., silicon carbide) respectively nitrides can also be
employed. Packed structures of metallic materials are mostly made
from wrappings of metal foils (e.g., FeCr alloy steel); it being
just as possible to stack webs or meshes of metal or the like into
a packed structure.
[0021] Advantageously, the packed structure features flow conduits
square in cross section having a cell density in the range 400 to
1200 cpsi, although it is just as possible that, instead of a
square cross-section, the flow conduits feature a hexagonal,
triangular, round or corrugated cross-section. The conduits may be
oriented parallel or at random (similar to a sponge). In addition
to the many and varied shapes featured by the packed structure, for
example, round, rectangular, racetrack, the possibilities for
configuring the cell densities also vary. For instance, cell
densities of around 400 cpsi are of advantage while cell densities
as high as approx. 1200 cpsi are just as possible at this time.
[0022] Usefully, the surface of the packed structure comprises, at
least in part, a coating as a catalyst. For example, a rare metal
coating may be provided. The surface of the flow conduits of the
packed structure can be increased (e.g., Washcoat: layer
thicknesses of a few .mu.m) by magnitudes and catalyst activated
for implementing catalyst reactions at technically relevant
reaction rates. The selectivity as to the wanted partial oxidation
products (e.g., CO and H.sub.2) can be enhanced by making use of a
suitable catalytically active packed structure for use in catalytic
production of hydrogen (partial oxidation, autothermic reforming,
steam reforming). Typical washcoat materials are oxides of
aluminum, silicon, titanium while typical catalysts includes rare
metals, such as, for example, Pt, Pd, Ni, etc.
[0023] Furthermore, it can be provided that the reaction zone is
followed by a homogenization zone. The products emerging from the
packed structure, for instance residual short-chain hydrocarbons,
hydrogen, carbon monoxide, water, carbon dioxide can be
reconditioned therein much easier into a homogenous mixture than as
compared to the fuel/air mixture upstream of the packed structure.
This is promoted, among other things, by the resulting diffusion
coefficients of the small molecular species (e.g., hydrogen)
produced and flame rates being significantly greater than as
compared to the long-chain components employed. The significantly
higher temperatures of the resulting components further improves
the material transport, and thus, the homogeneity. Due to the low
hydrocarbon concentration the tendency to soot clogging is low as
compared to the mixing chamber.
[0024] It also is useful to provide for the homogenization zone to
be followed by a further reaction zone. The resulting product
mixture can be further oxidized, e.g., by the addition of a further
oxidant flow to thus achieve air ratios up into the range of
combustion.
[0025] The device in accordance with the invention is further
rendered more useful in that it is operable in the mixing chamber
with a defined air ratio below 0.5, enabling the device to be put
to use without spontaneous ignition occurring and thus minimizing
the proportion of oxidation reactions and indirectly also the
degree of endothermic crack reactions in the mixing chamber.
Already ignited mixtures can be engineered to die away.
[0026] The device is furthermore improved to advantage by it
permitting operation in an evaporation zone between the evaporator
and the mixing zone at temperatures not exceeding, or only
insignificantly the end boiling point of the fuel used, which for
diesel fuel is approx. 360.degree. C. By not exceeding this
temperature the proportion of thermic crack products, resulting in
sooting up, is corresponding low. Due to the low temperatures there
is a minimum tendency of spontaneous self-ignition of the fuel/air
mixture. These low temperatures can also result in less soot being
formed by the kinetics being limited, than is to be expected by
thermodynamic equilibrium calculations.
[0027] Furthermore, preferably, the volume of the evaporation zone
and the mixing zone is engineered so that the residence times of
the fuel oxidant mixture, on average, are of the magnitude of the
reaction times of oxidation reactions, this again results in
minimizing the tendency of the fuel/air mixture to spontaneous
self-ignition. The short residence times can result in less soot
being formed because of the reduction in the contact time than is
to be expected by thermodynamic equilibrium calculations.
[0028] The invention is an improvement over the generic method in
that a packed structure is arranged in the reaction zone through
which the entire mixture, including the reaction products that have
already materialized, are passed. In this way, the advantages and
special features of the device in accordance with the invention are
also evident in the scope of a method, this applying likewise to
the preferred embodiments of the device in accordance with the
invention and the preferred method features resulting
therefrom.
[0029] The invention is based on having discovered that, by
providing a packed structure, particularly in conjunction with the
further features of the device, the drawbacks of prior art can now
be at least partially overcome. Thus, because the air ratio is set
defined in the mixing chamber, the evaporator can now be operated
so that low temperatures materialize there, so that spontaneous
self-ignition is avoided. These low temperatures diminish the
sooting tendency of the system, e.g., as prompted by cracking
reactions. The mixture forming zone and oxidation zone are now
practically separated, thus, doing away with the need for a mol
seal. The temperatures in the evaporator are very low and near
independent of output, thus correspondingly reducing the thermal
stress of the surrounding components. The hydrocarbons can now be
selectively partially oxidized in a first reaction stage by means
of a catalyst thus minimizing non-selective ways of reaction,
particularly cracking and soot forming.
[0030] Making use of a non-catalytic first reaction stage has the
advantage that the first reaction stage can now be operated at
higher temperatures since catalysts can deactivate at excessively
high temperatures. Because of the air ratio being defined,
engineered control of the formation of the wanted reaction products
is now possible. Unlike a naked flame in combustion reactions, all
gaseous or liquid hydrocarbon molecules as may be mixed with the
gas are now forced to reactingly flow through the packed structure
in this selected configuration. In conjunction with the high
temperatures., this results in very high conversion rates and
compact dimensions respectively. The hydrogen-rich gas mixture
having materialized in the first reaction stage can now be
homogenized much easier than the hydrocarbon/air mixture with near
zero soot being formed, because of the concentration of
hydrocarbons (potential crack candidates) being magnitudes smaller.
In addition homogenization can now be performed within a
significantly expanded operating range (at higher temperatures with
longer residence times), after which the hydrogen-rich gas mixture
can be supplied to a further reaction zone. Due to the mixture
being homogenous the corresponding reaction zone can now be
engineered highly compact thereby guaranteeing an homogenous
product gas composition. For instance, the hydrogen-rich gas
mixture can be further oxidized to be low in emissions. Because the
mixture is homogenized, the corresponding combustion
chamber/reaction chamber can now be dimensioned highly
compactly.
[0031] The invention will now be explained in detail by way of
particularly preferred example embodiments with reference to the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a diagrammatic representation of a first
embodiment of a system for providing a homogenous fuel/air mixture
on the basis of liquid fuel;
[0033] FIG. 2 is a diagrammatic representation of a second
embodiment of a system for providing a homogenous fuel/air mixture
on the basis of liquid fuel;
[0034] FIG. 3 is a graph plotting temperature and output curves as
a function of time as relevant to a device in accordance with the
invention; and
[0035] FIG. 4 is a graph plotting the free enthalpy of selected
hydrocarbons and of the elements carbon and hydrogen as a function
of temperature.
DETAILED DESCRIPTION OF THE INVENTION
[0036] In the following description of preferred embodiments of the
invention like reference numerals designate like or comparable
components.
[0037] Referring now to FIG. 1, there is illustrated a first
embodiment of a system for providing a homogenous fuel/air mixture
on the basis of liquid fuel. The core component of the system for
providing a homogenous fuel/air mixture on the basis of liquid fuel
as shown in FIG. 1, as an example, is the fuel evaporator 2
arranged in an evaporator element 1, attached to which is a
supporting element 3b for mounting a packed structure 3 which may
be jacketed by a fiber mat 3c for mechanical fixation and thermal
insulation respectively.
[0038] Liquid fuel and oxidant are supplied to the system via the
fuel feeder 5 and oxidant feeder 4 respectively. The oxidant,
preferably air, with optional additives, such as, e.g., steam,
enters via radially inwardly directed ports 6 into the mixing
chamber 12 where the oxidant is mixed with the fuel that has been
evaporated in an evaporation chamber 13 that is located upstream of
the mixing chamber 12. In general, the evaporation chamber 13 and
the mixing chamber 12 form a single unit, evaporation being more
likely to occur upstream and mixing downstream, although backflows
in the direction of the fuel evaporator may be provided so that
here too, fuel and air may be mixed.
[0039] Furthermore, as promoted by the low temperatures on the
non-woven metal fiber mat, evaporation of high boiling point
materials can occur incompletely in the evaporation chamber so that
this takes place in the mixing chamber 12 since the fuel flows in
the direction of the, for example, 900.degree. C packed structure
3. Oxidation of the fuel/air mixture occurs optionally by an
electric igniter 7 or by the packed structure. The homogenization
zone 8 adjoining the reaction zone 14 contained in the packed
structure 3 serves to homogenize the resulting products of
oxidation. The homogenized gas mixture can then be further
converted within the further reaction zone 9, e.g., by a supply of
oxidant via a further reactant/oxidant feeder 10. The way in which
this supply is engineered has a major influence on the material and
heat transport in the reaction zone 9. For example, by means of
port 11 the reaction products are transported to the wall so that
some of the reaction heat can be simply given off to the ambience
in thus preventing that the components downstream of the reaction
zone 9 become overheated.
[0040] Depending on what is required of the application, the system
for providing a fuel/air mixture can be operated at a variety of
ambient temperatures. With very high ambient temperatures
(>400.degree. C.) there is, however, the risk that too much heat
enters the fuel evaporator, prompting cracking reactions (e.g., in
the non-woven mat). Accordingly, moderate ambient temperatures are
of advantage in general. If, however, the application demands on
the fuel evaporator require it to be operated in a hot ambience,
providing for thermal insulation of the evaporator is of advantage
as described below. In this case, it is of advantage when the zones
identified 2a and 3b feature a low thermal conductivity, or to
engineer the heat conducted to the non-woven mat to be a minimum as
can be done, for example, by providing thin ridges in the zone
identified 2a. Furthermore, it may be of advantage to provide a
thermal insulator (not shown in FIG. 1), for instance a ceramic
disk, between the zones 2 and 3b. Also possible is thermal
insulation of the evaporator as may be applicable, this applying
likewise to the oxidant and fuel paths.
[0041] Referring now to to FIG. 2, there is illustrated a
diagrammatic representation of a second embodiment of a system for
providing a homogenous fuel/air mixture on the basis of liquid
fuel. Unlike the embodiment of FIG. 1, the supply of the oxidant
flow in the second reaction zone is multiply stepped and oriented
radially inwards via a plurality of ports 11.
[0042] Referring now to FIG. 3, there is illustrated a graph
plotting temperature and output curves as a function of time as is
relevant to a device in accordance with the invention. Shown are
the exemplary results obtained with such a system with diesel
evaporation in air. The packed structure 3 employed contains a
catalyst which partially oxidizes the diesel fuel so that a
hydrogen-rich gas mixture materializes. This can be made use of in,
e.g., an auxiliary power unit (APU) for generating electricity and
heat. FIG. 3 plots the temperatures as measured in the evaporator
chamber (curve a) and in the catalyst (curve b) for the thermal
outputs (curve c) between 1 and 4 kW and an air ratio of 0.3 to
0.35. As is evident, the temperature in the evaporation chamber is
approx. 300.degree. C. Despite the high temperature at the center
of the catalyst (max. 1100.degree. C.) no flashback of the fuel/air
mixture occurs within the mixing chamber. Even when the residence
time within the mixing chamber is increased (reduction in the
thermal output from oxidant feeder 4 to 1 kW) no ignition is
observed in thus achieving stable operation.
[0043] It is understood that the features of the invention as
disclosed in the above description, in the drawings and as claimed
may be essential to achieving the invention both by themselves or
in any combination.
* * * * *